1. Field of the Invention
The present invention relates to a relaying device and a communication system, which mediate communication between a transceiver and a telephone set over a network.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2011-135290 discloses a relaying device that enables verbal communication to be conducted between a wireless apparatus, such as a transceiver, and a telephone set over an IP telephone system having a network or over a wired phone line. The relaying device of this document operates in the following manner. First, the relaying device makes a SIP response in response to a call from a device at the other end, and continuously receives audio packets which the device at the other end has continuously sent over a network. Then, the relaying device determines whether or not an audio signal in the received audio packets has a higher level than a threshold at which an audio signal is regarded as a speech sound (VOX processing). If the level of the audio signal is higher than the threshold, the relaying device causes a repeater as a wireless relaying apparatus to enter a transmission state (VOX-ON), and transfers this audio signal to the repeater. In response, the repeater wirelessly sends the audio signal to a terminal.
Upon receiving a VOX-ON signal or a PTT-ON signal from the relaying device, the repeater first reserves a channel (wireless communication channel), and then starts sending the audio signal. In this case, specifically, the repeater cannot send the audio signal promptly upon receiving the PTT-ON signal, because it requires time to reserve a channel. If an idle channel is present, the repeater spends time of 100 ms or so to perform a processing of reserving a channel. Otherwise, if no idle channel is present, the repeater needs to wait for any idle channel to be made available.
However, a typical relaying device is configured to send an audio signal simultaneously with a VOX-ON signal, and thus a part of the audio signal which the repeater receives in the course of reserving a channel is discarded without being sent to a transceiver. As a result, there are cases where the beginning of the received audio signal is clipped off, and only the remaining part thereof is heard from the transceiver.